Is there any condition where you would ever consider a "cheating" partner/spouse "forgivable"?

As far as I know, cheating is one of the most hurtful thing a loved-one can do. Some believe that "Once a cheater, always a cheater." But I do know people (mostly women, but some men too) who forgave their spouse for cheating, or at least, stayed with them. Some of these cheaters never cheated again,... show more As far as I know, cheating is one of the most hurtful thing a loved-one can do. Some believe that "Once a cheater, always a cheater."
But I do know people (mostly women, but some men too) who forgave their spouse for cheating, or at least, stayed with them.
Some of these cheaters never cheated again, while a few just keep on cheating (and keep being forgiven).

Your thought on this?
Update: I said "one of the most hurtful things", so it's not necessarily the worst or the most hurtful.

For all I know, your partner can abuse you, lock you up, rape you, kill you, etc... and they're all just as bad, if not worse.
And there's probably a list of other more hurtful things.
Update 2: Sammy, how refreshing! So you finally honoured me with an answer instead of just a star. My opinion? Well, I've only been cheated once, and she didn't ask for forgiveness. I thought I was being the best spouse I could, but apparently that wasn't enough (whether financially? physically?... show more Sammy, how refreshing! So you finally honoured me with an answer instead of just a star.

My opinion?

Well, I've only been cheated once, and she didn't ask for forgiveness. I thought I was being the best spouse I could, but apparently that wasn't enough (whether financially? physically? romantically? I don't know).
I would've given her a second chance, but she didn't want it. What's a man to do?

A friend of mine, however, had her husband accused her of cheating and left the house to be with his ex. She, too, would probably give this s.o.b. a second chance, but he didn't ask for it. What's a girl to do?
Update 3: amber3_6:
I totally understand.
I kinda have this type of relationship too (this "someone you've known for years and is always in your mind though you both have relationships with others"). And just like what you wrote, we both failed those relationships so far.
Update 4: Barbawhiskey:
how many hours do I spend worrying?

In my case, None.
I trusted her completely.
She betrayed that.
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